Traditional skin grafting is accomplished by taking a thin slice of dermal tissue from a donor site in order to cover a wound site, such as a burn area. In some instances, the slice of dermal tissue is meshed to expand its size, creating a meshed graft. Traditional devices used to harvest the tissue from the donor site include dermatomes for removing a thin slice of the upper layers of skin from a donor site. The slice is then meshed using traditional techniques to create and expand the sheet of skin tissue that gives the slice a weave-like appearance. The purpose of expanding the skin from the donor site is to increase the amount of area on a recipient site that can be covered by the donor site. Some of the most desirable expansion ratios currently available are 6:1. That is, under the most ideal conditions, skin taken from a donor site would be able to cover a recipient site that is six times larger than the donor site.
Traditional meshed grafting techniques have been shown to yield 90% viability at the donor site. A slightly lower viability rate occurs for non-meshed sheet grafts, mostly due to fluid accumulation under the sheet graft. Factors that lead to graft failure include poor circulation, unclean wounds, patient interference with the graft dressing, obesity, and smoking. Additionally, in at least approximately 10% of cases, infection at the donor site occurs. Although such donor site infections are not likely related to graft failure at the wound site, they still pose problems for both the patient and caregiver.
As mentioned, traditional meshing techniques yield a most favorable expansion ratio of 6:1. For example, a 1 cm2 donor site can cover a 6 cm2 wound site. While greater ratios of 9:1 and 12:1 may be possible using meshing techniques, there is also a significant delay in epithelialization with such ratios.
Micro grafting techniques, in which the donor tissue is actually minced in order to achieve a greater than 10:1 expansion ratio, are known in the art. Such techniques allow for a much greater coverage area from a small donor site. However, traditional techniques are cumbersome, and often the viability of the cells is compromised to such an extent that sometimes less than 50% of the cells are viable when applied to the wound site. Additionally, traditional techniques have thus far been inadequate in producing viable cells in the range of 500-1500 microns.
Traditional micrograft techniques, dating back to 1963, utilized minced skin that is between ⅛th inch (approximately 3 mm, or 3000 microns) or 1/16th inch (approximately 1.5 mm, or 1500 microns) in size. However, disadvantages of using pieces larger than 1500 microns have been noted. Among the disadvantages are that many of the cells are trapped within the pieces of skin, and are thus unable to proliferate or produce new cells required to form new skin. Furthermore, if such large pieces of skin are to be transplanted, the epidermis side of each piece has to be oriented upwards, and the dermis side oriented downwards. This makes the procedure tedious and impractical. Also, the appearance of the new skin that is produced using particles of this size is poor, often having a cobblestone appearance.
Other micrografting techniques have utilized minced skin that is 200 to 500 microns in size. While sometimes producing cosmetically better grafts over the larger micrografts, many of the cells contained in the particles are rendered non-viable by the process of producing cells of such a small size.
It is therefore an object of this invention to provide a system for obtaining and processing tissue samples from a donor site on the order of 50-1500 microns in size, such that the vast majority of tissue processed at this size is viable when transplanted to a recipient site. It is a further object of the present invention to strike the ideal balance between cell viability and cell proliferation between the size range of 500-1500 microns, and most preferably 600 microns, which has heretofore not been achieved.
Additional objects of the present invention include a significant reduction in the size of the donor site as compared to traditional mesh-graft procedures; minimizing scarring of the graft site as compared to traditional mesh-graft procedures; improvement of the pliability of tissue in the graft site; improvement of the cosmetic appearance of the graft site as compared to current methods; and improvement of graft “take.”